Building block for a toy building set



FIG. 1 is a top perspective view of a building block for a toy building set showing my new design;

FIG. 2 is a left side elevational view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a rear elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof. 

The ornamental design for a building block for a toy building set, as shown and described. 